Method for extracing bitumen from an oil sand feed stream

ABSTRACT

The present invention provides a method for extracting bitumen from an oil sand feed stream, the method including at least the steps of: (a) providing an oil sand feed stream; (b) contacting the oil sand feed stream with a hydrocarbon solvent thereby obtaining a solvent-diluted oil sand slurry; (c) filtering the solvent-diluted oil sand slurry thereby obtaining a solids-enriched stream and a filtrate; and (d) removing at least a part of the hydrocarbon solvent from the solids-enriched stream thereby obtaining a solvent-depleted solids-enriched stream, wherein in step (d) the at least part of the hydrocarbon solvent is removed from the solids-enriched stream by purging with a gas stream at a gas/solids weight ratio (related to the solids-enriched stream) of at most 3.0%.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/927,805 filed Jan. 15, 2014, which is incorporated herein by reference.

BACKGROUND

The present invention relates to a method for extracting bitumen from an oil sand. Various methods have been proposed in the past for the recovery of bitumen (sometimes referred to as “tar” or “bituminous material”) from oil sands as found in various locations throughout the world and in particular in Canada such as in the Athabasca district in Alberta and in the United States such as in the Utah oil sands. Typically, oil sand (also known as “bituminous sand” or “tar sand”) comprises a mixture of bitumen (in this context also known as “crude bitumen”, a semi-solid form of crude oil; also known as “extremely heavy crude oil”), sand, clay minerals and water. Usually, oil sand contains about 5 to 25 wt. % bitumen (as meant according to the present invention), about 1 to 13 wt. % water, the remainder being sand and clay minerals.

As an example, it has been proposed and practiced at commercial scale to recover the bitumen content from the oil sand by mixing the oil sand with water and separating the sand from the aqueous phase of the slurry formed. Disadvantages of such aqueous extraction processes are the need for extremely large quantities of process water (typically drawn from natural sources) and issues with removing the bitumen from the aqueous phase (whilst emulsions are being formed) and removing water from the bitumen-depleted sand.

Other methods have proposed non-aqueous extraction processes to reduce the need for large quantities of process water. An example of such a non-aqueous extraction process is disclosed in e.g. US 2013/0068664.

There is a continuous desire to improve the process efficiency in methods for extracting bitumen from an oil sand feed stream.

SUMMARY OF THE INVENTION

The present invention provides a method for extracting bitumen from an oil sand feed stream, the method comprising at least the steps of:

-   (a) providing an oil sand feed stream; -   (b) contacting the oil sand feed stream with a hydrocarbon solvent     thereby obtaining a solvent-diluted oil sand slurry; -   (c) filtering the solvent-diluted oil sand slurry thereby obtaining     a solids-enriched stream and a filtrate; and -   (d) removing at least a part of the hydrocarbon solvent from the     solids-enriched stream thereby obtaining a solvent-depleted     solids-enriched stream,

wherein in step (d) said at least part of the hydrocarbon solvent is removed from the solids-enriched stream by purging with a gas stream at a gas/solids weight ratio (related to the solids-enriched stream) of at most 3.0%.

It has now surprisingly been found according to the present invention that significantly reduced residual hydrocarbon solvent levels can be obtained for the extracted sand (the solvent-depleted and solids-enriched stream obtained in step (d)) in a surprisingly simple and efficient manner It has in particular surprisingly been found according to the present invention that by using a relatively small amount of purge gas to remove the hydrocarbon solvent an effective hydrocarbon solvent removal is obtained. Also, when a lower purge gas rate is used, the concentration of hydrocarbon solvent in the removed purge gas stream will be relatively high such that a smaller purge gas recycling unit is required. Without wanting to be bound to a specific theory it is believed that by using a relatively small amount of purge gas, this will result in a reduced evaporation of any water present in the solids-enriched stream and hence also a reduced cooling down of the solids-enriched stream. This reduced cooling down of the solids-enriched stream results in higher hydrocarbon solvent evaporation rates.

DETAILED DESCRIPTION

According to the present invention, the providing of the oil sand feed stream in step (a) can be done in various ways. Typically, before contacting the dry oil sand feed stream (which may contain some water being present in the oil sand) with the solvent, the oil sand particles are reduced in size, e.g. by crushing, breaking and/or grinding, to below a desired size upper limit Experience in large scale operations shows that the achievable size upper limit for such size reduction is currently about 8 inch.

The contacting of the oil sand feed stream in step (b) with the hydrocarbon solvent thereby obtaining a solvent-diluted oil sand slurry is not limited in any way. As an example, the hydrocarbon solvent may be added before, during or after the size-reducing step (if available) of the oil sand feed stream. Further size reduction in the presence of the hydrocarbon solvent may be performed; part of the size reduction may take place by dissolution of bitumen present in the oil sand, but further size reduction e.g. by using screens and/or again crushers, breaker or grinders may be performed, if desired.

Although the hydrocarbon solvent as used in the method of the present invention is not limited in any way, it is typically a saturated or unsaturated aliphatic (i.e. non-aromatic) solvent and may include linear, branched or cyclic alkanes and alkenes and mixtures thereof. Typically, the hydrocarbon solvent (or solvents) has (have) a boiling point of at most 100° C., preferably at most 80° C., more preferably at most 60° C., even more preferably at most 40° C. Preferably, the hydrocarbon solvent used in step (b) comprises a hydrocarbon having from 3 to 9 carbon atoms per molecule, more preferably from 4 to 7 carbons per molecule, or a combination thereof. Especially suitable hydrocarbon solvents are saturated aliphatic hydrocarbons such as propane, butane, pentane, hexane, heptane, octane and nonane (including isomers thereof), in particular pentane and cyclopentane. Preferably, the hydrocarbon solvent used in step (b) comprises an aliphatic hydrocarbon, preferably a aliphatic hydrocarbon having 3 to 9 carbon atoms per molecule.

Preferably, the hydrocarbon solvent used in step (b) comprises at least 90 wt. % of an aliphatic hydrocarbon having 3 to 9 carbon atoms per molecule (and preferably of a compound selected from the group consisting of pentane and cyclopentane or a combination thereof), preferably at least 95 wt. %. Also, it is preferred that in step (b) substantially no aromatic solvent (such as toluene or benzene) is present, i.e. less than 5 wt. %, preferably less than 1 wt. %.

Typically, the solvent-diluted oil sand slurry obtained in step (b) has a solvent-to-bitumen (S/B) weight ratio of above 0.5, more typically above 0.7, and typically below 5.0, more typically below 4.0. Preferably, the solvent-diluted oil sand slurry has a solvent-to-bitumen (S/B) weight ratio of above 1.0, preferably from 1.2 to 5.0, more preferably from 1.4 to 3.0, even more preferably from 1.6 to 2.5. Further it is preferred that the solvent-diluted oil sand slurry obtained in step (b) comprises from 25 to 60 vol. % of solids, preferably from 32 to 60 vol. % of solids, more preferably from 35 to 50 vol. %, even more preferably from 40 to 48 vol. %.

After contacting the oil sand with the solvent in step (b), the solvent-diluted oil sand slurry is filtered in step (c), thereby obtaining a solids-enriched stream (containing the extracted sand) and a filtrate. This filtering step can be performed in many different ways. Typically, the solvent-diluted oil sand slurry is deposited as a filter cake on top of a filter medium, wherein during filtering the pressure above the filter cake is preferably at least 1.7 bara. The filter medium can be varied in many ways, but is typically a wire mesh, wedge wire, cloth, membrane or the like. The major part of solids in the filter cake does not pass through the filter medium, while liquids do. Fresh solvent and/or solvent vapour/liquid and/or inert gases (such as steam or N₂) may be passed through the filter cake by means of an applied pressure difference between the space above the top of the filter cake and the space below the filter medium. The filtrate that is obtained after passage through the filter medium may comprise some dispersed fine solids. The solids particles in the filter cake are left on top of the filter medium and removed from the filter for further processing.

Of course, the filtering in step (c) can be varied in many ways without departing from the scope of the invention. As an example, instead of one filtrate, two or more filtrates having different S/B weight ratios may be obtained. Although some fresh solvent may be used at the start-up of the process of the present invention, the addition of fresh solvent later on is preferably kept to a minimum; to this end it is preferred that most of the solvent used in the filtration step is recycled from downstream of the process.

As mentioned above the solvent-diluted oil sand slurry is filtered in step (c), whilst the pressure above the filter cake is preferably at least 1.7 bara (i.e. the space in the filtration unit above the top of the filter cake has a pressure of above 1.7 bara).

According to an especially preferred embodiment of the present invention, this (over-)pressure above the filter cake during step (c) is provided by hydrocarbon solvent vapour (which hydrocarbon solvent vapour condenses in and passes through the filter cake during the filtering). The use of solvent vapour during the filtering of step (c) is very effective in washing bitumen from the filter cake, resulting in increased bitumen recovery. If desired, before applying the over-pressure on the filter cake, first a layer of liquid hydrocarbon solvent may be applied to further assist the washing of the bitumen from the filter cake.

Preferably, during the filtering in step (c) the pressure above the filter cake is in the range of from 1.7 to 5.0 bara, preferably from 2.0 to 4.5 bara, more preferably from 2.2 to 4.3 bara, even more preferably from 2.4 to 4.0 bara.

In general it is preferred that during the filtering in step (c) the pressure difference over the filter cake is below 4.0 bar, preferably below 3.5 bar, more preferably below 3.0 bar and typically above 0.1 bar.

Typically, the solvent-diluted oil sand slurry has a temperature when deposited as a filter cake on the filter medium in step (c) of from 5 to 50° C., preferably from 7 40° C. If desired, the filter cake may be heated up before or during the filtering in step (c). In case an aliphatic hydrocarbon having 5 carbon atoms per molecules (such as iso-pentane or in particular n-pentane or cyclopentane) is used as the solvent, it is preferred that the solvent-diluted oil sand slurry is filtered in step (c) at a temperature in the range of from 35° C. to 120° C., preferably from 40° C. to 100° C. Part of the heat may originate from the condensing hydrocarbon solvent vapour (if any) used for creating the over-pressure. The person skilled in the art will understand that there may be a temperature gradient over the filter cake.

It is preferred that, after the filtration of step (c), the pressure of the solids-enriched stream (i.e. the filter cake that is left on the filter medium once the filtering has taken place and is removed subsequently) obtained in step (c) is lowered to below 1.2 barg, preferably to below 1.0 barg, more preferably below 0.5 barg, even more preferably below 0.3 barg, yet even more preferably below 0.1 barg. Typically, this lowering of pressure (to obtain a ‘flashed solids-enriched stream’, typically containing from 0.01 to 1.0 wt. %, more typically at least 0.05 and at most 0.7 wt. %, residual hydrocarbon solvent) takes place before purging with the gas stream in step (d) takes place. Typically, the lowering of the pressure of the solids-enriched stream to below 1.2 barg takes place outside the filtering unit in a dedicated depressurizing unit. Such a depressurizing unit may be embodied in various ways and may comprise e.g. one or more batch-operated vessels, lock hoppers, rotary valves, etc.

According to a preferred embodiment of the method of the present invention hydrocarbon solvent is removed from the filtrate thereby obtaining a bitumen-enriched stream. Typically the bitumen-enriched stream is further processed and for example sent to a refinery for upgrading. Preferably, at least part of the removed hydrocarbon solvent is reused in the filtering of step (c).

In step (d), at least a part of the hydrocarbon solvent is removed from the solids-enriched stream thereby obtaining a solvent-depleted solids-enriched stream, wherein said at least part of the hydrocarbon solvent is removed from the solids-enriched stream by purging with a gas stream at a gas/solids weight ratio (related to the solids-enriched stream) of at most 3.0%.

According to an especially preferred embodiment according to the present invention, in step (d) the hydrocarbon solvent is removed by purging with the gas stream at a gas/solids weight ratio (related to the solids-enriched stream) of at most 2.0%, preferably at most 1.0%, more preferably at most 0.5%.

Preferably, the solvent-depleted solids-enriched stream obtained in step (d) comprises at least 1.0 wt. % water, based on the solvent-depleted solids-enriched stream, preferably at least 2.0 wt. %. Typically, solvent-depleted solids-enriched stream obtained in step (d) comprises at most 15.0 wt. %, preferably at most 12 wt. %, more preferably at most 10.0 wt. %.

Also it is preferred that the solvent-depleted solids-enriched stream obtained in step (d) has a water content (relative to present mineral solids) that is at most 1.0 wt. % lower than the water content of the oil sand feed stream provided in step (a).

Further it is preferred that the solvent-depleted solids-enriched stream obtained in step (d) has a hydrocarbon solvent content of at most 0.025 wt. % (i.e. 250 ppmw), preferably at most 0.010 wt. % (i.e. 100 ppmw).

The person skilled in the art will readily understand that the composition of the purge gas can be widely chosen. Typically it is an inert gas, preferably steam, a flue gas or N₂ or a mixture thereof.

The person skilled in the art will readily understand that the removing of the hydrocarbon solvent from the solids-enriched stream in step (d) may be performed in a rotary dryer. Because the water content of this stream is not significantly reduced, depending on the actual water content of this stream, build-up in the rotary dryer (e.g. on the walls thereof) may occur. This build-up may be mitigated by the following means:

External Agitators, such as knockers along the outer shell of the rotary dryer.

Internal agitators; e.g. loose chains attached to the lifters used in rotary dryers, or addition of steel balls or other milling agents.

Special lifter design.

Materials of construction of the rotary dryer, e.g. using low-friction surfaces.

Flexible rubber internals that will bend under gravity, and mitigate bridging of solids in that way.

The present invention is described below with reference to the following Examples, which is not intended to limit the scope of the present invention in any way.

EXAMPLE 1

In order to obtain a (flashed) solids-enriched stream having a composition representative for such a stream obtained after contacting an oil sand feed stream with a hydrocarbon solvent to obtain a solvent-diluted slurry and subsequently filtering the solvent-diluted slurry to obtain the solids-enriched stream (and flashing off the bulk of the hydrocarbon solvent, i.c. n-pentane), the following was done.

A 1.11 dryer was filled with 350 g dried extracted oil sand (comprising about 94.8 wt. % solids (sand/clay), about 1.2 wt. % bitumen and about 4 wt. % water). After adding 30.3 g n-pentane the dryer was closed (using a ball valve) and purged with nitrogen for 2 minutes. After the purging, the sand was stirred at 80 rpm with an anchor stirrer for 30 minutes at room temperature. The dryer was then lowered in a hot water bath (70° C.) and stiffing at 80 rpm was continued until the temperature inside the dryer was 70° C. (the vapour pressure of n-pentane and the nitrogen present was about 3.8 bara at 70° C.).

Then, the dryer was removed from the water bath and the ball valve was opened. The n-pentane was flashed to atmospheric pressure via a vessel filled with stainless steel balls (diameter of 3 mm) that were put in a freezer at −18° C. before use. The bulk of the n-pentane condensed in the vessel. When the dryer was at atmospheric pressure, it was placed horizontally and the stirring speed was lowered to 20 rpm.

Solids samples of the flashed solids-enriched stream were taken immediately after the flash and at regular intervals during the subsequent process of removal of residual pentane. The solids samples were taken via a sample probe and immediately dropped into a 250 ml bottle containing 40 ml of a mixture of 74 vol. % toluene, 26 vol. % isopropylalcohol and a trace amount (0.5 g) methylcyclohexane (the latter used as internal standard for calibration purposes); afterwards the liquid phases of these bottles were analyzed for residual pentane, bitumen and water content. The composition and properties of the solids samples of the flashed solids-enriched stream (directly after flashing) was as listed in Table 1 below.

TABLE 1 Fines (particles having a diameter <44 μm; using 10 laser diffraction) [wt. %] Water content (using Karl-Fisher titration) 2.8 [wt. %] Bitumen content (using gravimetric analysis) 1.2 [wt. %] Pentane content (using GC analysis) [wt. %] 0.5 Temperature [° C.] 45 Pressure [bara] atmospheric

Directly after flashing, the flashed solids-enriched stream was purged with a nitrogen flow of 0.35 1/min The time to remove the hydrocarbon solvent from the solids-enriched stream to a level of 0.025 wt. % was 5 minutes using 6.5 1 purge gas per kg of sample; this corresponds to a gas/solids weight ratio (related to the solids-enriched stream) of 0.6%.

Comparative Example 1

The procedure of Example 1 was repeated to obtain the flashed solids-enriched stream having the composition and properties as listed in Table 1.

The flashed solids-enriched stream was transferred to a lab-scale fluidized bed dryer (Model ConsiGma™; obtainable from GEA Pharma Systems AG, Bubendorf, Switzerland) whilst removing hydrocarbon solvent by purging with a N₂ gas stream as a purge gas. The time to remove the hydrocarbon solvent from the solids-enriched stream to a level of 0.025 wt. % was 5 min using 600 1 purge gas per kg of sample; this corresponds to a gas/solids weight ratio (related to the solids-enriched stream) of 75%.

Discussion

As can be seen from Example 1 and Comparative Example 1, the method according to the present invention provides a surprisingly simple way of removing the hydrocarbon solvent from the solids-enriched stream obtained after filtration. By applying a relatively low purge gas rate (corresponding to a gas/solids weight ratio 0.6% in Example 1 versus 75% in Comparative Example 1), this surprisingly results in a similar drying time of the solids-enriched stream (thereby obtaining a solvent-depleted solids enriched stream). However, as less purge gas is used according to the present invention for the hydrocarbon solvent removal, subsequent processing thereof is also minimized, making the hydrocarbon solvent removal more efficient.

The person skilled in the art will readily understand that many modifications may be made without departing from the scope of the invention. 

We claim:
 1. A method for extracting bitumen from an oil sand feed stream, the method comprising at least the steps of: (a) providing an oil sand feed stream; (b) contacting the oil sand feed stream with a hydrocarbon solvent thereby obtaining a solvent-diluted oil sand slurry; (c) filtering the solvent-diluted oil sand slurry thereby obtaining a solids-enriched stream and a filtrate; and (d) removing at least a part of the hydrocarbon solvent from the solids-enriched stream thereby obtaining a solvent-depleted solids-enriched stream, wherein in step (d) said at least part of the hydrocarbon solvent is removed from the solids-enriched stream by purging with a gas stream at a gas/solids weight ratio (related to the solids-enriched stream) of at most 3.0%.
 2. The method according to claim 1, wherein the hydrocarbon solvent used in step (b) comprises a hydrocarbon having from 3 to 9 carbon atoms per molecule.
 3. The method according to claim 1, wherein the hydrocarbon solvent used in step (b) comprises an aliphatic hydrocarbon having 3 to 9 carbon atoms per molecule.
 4. The method according to any claim 2, wherein the hydrocarbon solvent used in step (b) comprises at least 90 wt. % of an aliphatic hydrocarbon having 3 to 9 carbon atoms per molecule.
 5. The method according to claim 1, wherein in step (c) the solvent-diluted oil sand slurry is deposited as a filter cake on a filter medium and wherein during filtering the pressure above the filter cake is at least 1.7 bara.
 6. The method according to claim 5, wherein the pressure of the solids-enriched stream obtained in step (c) is lowered to below 1.2 barg.
 7. The method according to claim 5, wherein the pressure of the solids-enriched stream obtained in step (c) is lowered to below 0.1 barg.
 8. The method according to claim 5, wherein during the filtering in step (c) the pressure above the filter cake is in the range of from 1.7 to 5.0 bara.
 9. The method according to claim 5, wherein during the filtering in step (c) the pressure above the filter cake is in the range of from 2.4 to 4.0 bara.
 10. The method according to claim 5, wherein during the filtering in step (c) the pressure difference over the filter cake is below 4.0 bar.
 11. The method according to claim 5, wherein during the filtering in step (c) the pressure difference over the filter cake is below 3.0 bar.
 12. The method according to claim 1, wherein hydrocarbon solvent is removed from the filtrate thereby obtaining a bitumen-enriched stream.
 13. The method according to claim 1, wherein in step (d) the hydrocarbon solvent is removed by purging with the gas stream at a gas/solids weight ratio (related to the solids-enriched stream) of at most 2.0%.
 14. The method according to claim 1, wherein in step (d) the hydrocarbon solvent is removed by purging with the gas stream at a gas/solids weight ratio (related to the solids-enriched stream) of at most 0.5%.
 15. The method according to claim 1, wherein the solvent-depleted solids-enriched stream obtained in step (d) comprises at least 1.0 wt. % water, based on the solvent-depleted solids-enriched stream.
 16. The method according to claim 1, wherein the solvent-depleted solids-enriched stream obtained in step (d) comprises at least 2.0 wt. % water, based on the solvent-depleted solids-enriched stream.
 17. The method according to claim 1, wherein the solvent-depleted solids-enriched stream obtained in step (d) has a water content (relative to present mineral solids) that is at most 1.0 wt. % lower than the water content of the oil sand feed stream provided in step (a).
 18. The method according to claim 1, wherein the solvent-depleted solids-enriched stream obtained in step (d) has a hydrocarbon solvent content of at most 0.025 wt. %.
 19. The method according to claim 1, wherein the solvent-depleted solids-enriched stream obtained in step (d) has a hydrocarbon solvent content of at most 0.010 wt. %. 